Wireless devices use radio frequencies (RF) to transmit information. For example, cell phones use amplified RF to transmit voice and data signals to base stations, which allows signals to be relayed to communication networks. Other existing wireless communication devices include Wifi, Bluetooth, WLAN, 3G/4G devices, UMTS and its Long-Term Evolution (LTE) . . . .
In a conventional wireless device, the power amplifier consumes most of the power of the overall wireless system. For systems that run on batteries, a power amplifier with a low efficiency results in a reduced communication time for a given battery life. In addition, a decrease in efficiency results in increased requirements for heat removal, which may increase the equipment and operating costs and may decrease the life time of some components. Furthermore, saving energy is a tremendous need for communication operators contributing to the green movement.
For this reason, much effort has been expended in increasing the efficiency of RF power amplifiers.
A commonly used type of amplifier is the Doherty-type power amplifier.
This type of power amplifier was designed by W. H. Doherty in 1936.
During decades, the modulation schemes (AM and FM) employed required linear amplification. Despite its good efficiency, the Doherty amplifier was not used because of its nonlinearity.
In recent years, the resurgence of popularity of the Doherty amplifier is based on its very high power-added efficiency when amplifying input signals with high PAR (Peak-to-Average Ratio), like for instance OFDM (Orthogonal Frequency Division Multiplexing) signals. In such contexts, the reasonable non-linearity of the Doherty amplifier can be compensated by analog and digital techniques.
However, it is still desirable to improve further the efficiency of the power amplifier of a telecommunication device, notably for the reasons mentioned previously.